Plot confidence interval for the slope
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Hi all,
I've been looking for an answer for a while, but it seems nobody asked it before.
So : I have a linear regression. I can find the confidence interval of the slope with the regress function. It gives me 2 numbers (for the slope). Of course. But how to plot it ? I mean, plots of the "confidence interval of the slope" look like curves when I google it. How do I obtain those curves ?
Thank you very much for your help !
Lucile
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Accepted Answer
Wayne King
on 3 Dec 2012
Edited: Wayne King
on 3 Dec 2012
You will get more than the confidence interval of the slope. In a simple linear (1st order) regression model, keep in mind that you will have a confidence interval for the intercept and the slope terms. You can plot those lines as confidence bounds, see the following example
load carsmall
x1 = Weight;
y = MPG;
X = [ones(size(x1)) x1];
[b,bint] = regress(y,X)
xval = min(x1):0.01:max(x1);
yhat = b(1)+b(2)*xval;
ylow = bint(1,1)+bint(2,1)*xval;
yupp = bint(1,2)+bint(2,2)*xval;
plot(x1,y,'k*');
hold on;
plot(xval,ylow,'r-.');
plot(xval,yupp,'r-.');
plot(xval,yhat,'b','linewidth',2);
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